Specific heat capacity
- E= MCAT
- The specific heat capacity, c, of a substance is the amount of energy needed to raise the temperature of 1kg of the substance by 1K
- Units of specific heat capacity: j kg-1 K-1 or j kg-1 C-1
The effect that transferred heat has on the temperature of an object depends on:
- amount of heat energy transferred
- mass of the object
- specific heat capacity of material from which object is made
Measuring the specific heat capacity
- Heat substance with heater
- accurate value for c? need a temperature rise of 10K
- (To improve accuracy start below room temperature and finish above to cancel out gains and losses)
- E = VIt
- put data into E= MCAT
- value for c is probably too big - some energy from the heater is transferred to air and the container.
Internal energy is the sum of the kinetic and potential energy of the particles within a system
as the temperature of the gas increases,:
- av. particle speed increases
- max. particle speed increases
- the distribution curve becomes more spread out.
energy is constantly transferred between particles in collisions, but the total energy of the system dosen't change. > the average speed of the particles stays the same provided the temperature does.
mean square speed: represents the squared speed of a typical particle.
average Ek is proportional to absolute temperature --> internal energy must also be dependent on absolute temperature.
For a constant mass of gas at a constant temperature, the pressure exerted by the gas is inversely proportional to the volume it occupies.
For a constant mass of gas at a constant pressure, the volume occupied by the gas is proportional to its absolute temperature
The pressure law:
For a constant mass of gas at a constant volume, the pressure exerted by the gas is proportional to its absolute temperature.
- If accurate experiments are carries out with a variety of gasses, the gas laws are not perfectly followed.
- e.g gas volume cannot be reduced to less than the volume of its molecules, but charles's law suggests that it would be at 0 kelvin.
An ideal gas (one which obeys the three gas laws perfectly) would have the following properties:
- molecules which have 0 size
- identical molecules
- molecules that collide with each other and the walls of their containers without any loss of energy in collisions that take 0 time
- molecules exert no forces on each othe except during collisions
- there are enough molecules for statistics to be applied.
The three gas laws can be combined to form the ideal gas equation: pV = NkT or pV=nRT
N = number of molecules of gas, K = boltzmann constant
R= universal gas constant, n = number of moles of gas
Investigating the gas laws
- length of air in vertical column represents volume of gas
- pressure measured using barometer
- pressure against 1/v graph gives straight line > inversley proportional.
The pressure law:
- data-log measurments of gas pressure and temperature
- pressure against absolute temperature gives straight line through origin > directly proportional.
- Adding thermal energy to an object raises its temperature (as long as it dosen't change state)
- All molecules in a sample move randomly with a bariety of speeds/ The temperature of a sample is a measure of the average Ek of its molecules.
- If you took all of the kinetic energy out of a sample, its temperature couldn't fall further. This is absolute 0.
- If A and B are placed next to each other and energy (called thermal energy/heat) moves from one to the other, A started at a higher temperature.